Lifting Heavy Lights

[WiLL]

Is the difference possibly in the difference between lifting and **lifting**? As in lifting it by hand, where the body is unlikely to suddenly apply a shock loading to the unit, and **lifting** (perhaps better described as Hoisting?) where a chain motor could apply an impulse load to the unit that the handle isn't designed to withstand? From memory isn't it good practice to leave 25% capacity on a motor point to cover the start up impulse loading - I.e a max of 750Kg on a 1T point?

 

Just a thought!

 

And there's something in me that feels wrong about hanging a fixture from a motor and hoisting it aloft. I've no idea why!!

 

 

Well, I was talking a manual hoist anyway. Trust me there is no 'sudden' anything in a 6m manual hoist. It takes me about 10 minutes to get the units up to bar height!

[paulears]

I was wondering about the lifting by handles comments, initiated by Bryson's query. In almost every case unloading operation I do, the stress on the handles is far more than a plain lift. Unless it's just me, the friction in foam lined cases means that you take a deep breath on your side, and assuming somebody else is doing the other side, they do the same, you then do a very quick pull to overcome the stiction, or else the thing lifts a few inches and drops down again. The initial force applied to get them out is a lot more than that needed to simply lift the dead weight - and I don't see handles snapping off all over the place - indeed, I've never seen a handle snap when being used to lift a mover. Has anyone?

[kitlane]

Is the difference possibly in the difference between lifting and **lifting**? As in lifting it by hand, where the body is unlikely to suddenly apply a shock loading to the unit, and **lifting** (perhaps better described as Hoisting?) where a chain motor could apply an impulse load to the unit that the handle isn't designed to withstand? From memory isn't it good practice to leave 25% capacity on a motor point to cover the start up impulse loading - I.e a max of 750Kg on a 1T point?

 

Just a thought!

 

And there's something in me that feels wrong about hanging a fixture from a motor and hoisting it aloft. I've no idea why!!

 

That would make it a 750kg motor then wouldn't it? They say 1t on the side for a reason.

 

 

Lx Dad

 

To be fair he was talking about the point, not the motor. Motors are designed with the dynamic load in mind but can we be sure the same is true of the rigging points? Clearly, there should be a considerable safety factor and the point should be tested to well above its SWL but whereas a motor is almost certainly manufactured by an experienced company, a rigging point might be installed by someone who isn't an expert. So perhaps it is reasonable to make an allowance for dynamic load on a rigging point. 800kg times 125% = 1T.

[Simon Lewis]

If you were to take a parallel look at loudspeaker cabinet handles, they are obviously designed to take the weight of lifting, and be subject to quite high forces. However, no decent rigger would suspend a loudspeaker from its handles. I have broken several plastic and metal handles over the years, and have the usual photo library of other people's badly installed speakers that every one pokes fun at.

 

In the ML example, the difference is surely that when carrying out normal lifting and maneovering the device is only a few feet from the ground. A handle failure is unlikely to be catastrophic in such circumstances. Furthermore, if the handle was a structural member capable of taking a dynamic load (with the exception of those devices where this is a design feature) there wouldn't be the need to provide a specific secondary attachment point by the omega plate?

 

I agree that it's not likely for a handle to fail, but can sympathise with the sentiment that the handles are not meant for formal lifting per se.

 

Simon

[son of lx dad]

From memory isn't it good practice to leave 25% capacity on a motor point to cover the start up impulse loading - I.e a max of 750Kg on a 1T point?

 

I disagree Dad. I think Pete is along the right lines. There are a good many riggers who would consider putting a 2 ton in for an 800kg point when considering snatch loads as a factor in the design such as the truss also being accessed by a climber or the truss being used to sub hang motors for screens.

[jonathanhill]

We tour 1t Lodestars, 2ton SpanSets, 3 1/4ton shackles, 2ton shortening clutches and 12mm poly-wrapped steels for the FoH truss that weighs about 650kg over two or three points dependant on span and venue.

 

The tackle for the ladder points is 2ton shackles, 1/2ton chain hoists and 8mm poly-wrapped steel for 125kg per point ladders.

[Pete McCrea]

Trust me I've spent enough time under manual blocks to feel your pain. And because I run an AV business doesn't necessarilly mean I have no real rigging expirience- I do, and have worked as a house rigger and rigging crew on some decent sized shows. Add in a degree in Civil Engineering, so I'm not a neewbie. But I'm also not a NRC passed touring rigger too.

 

As for the whole handles thing - Im still undecided. Maybe it's a question that needs a definitive answer from Martin or Robe. Who's the Martin Rep on here?